This invention relates to a device that supplies oxygen to oxygen tuyeres provided in the hearth bottom or in the lower portion of the hearth side walls of a steel converter vessel. More particularly, it relates to the structure of an oxygen passage provided in the bearing section of a trunnion ring.
In that portion of a trunnion ring from which a trunnion shaft projects, generally, there are provided a horizontal opening extending in the same direction as the shaft and a vertical opening communicating with the horizontal one. A horizontal pipe is inserted in the horizontal opening so as to communicate with a rotary joint attached to one end of the shaft, and a vertical pipe is inserted in the vertical opening so as to communicate with the horizontal pipe.
To prevent the leakage of oxygen, the connecting structure and vertical pipe, provided where the horizontal and vertical openings meet, have conventionally been covered with an O-ring or other suitable sealing means. Nevertheless, oxygen leakage has not been completely prevented because of the large diameter of the vertical pipe, approximately 150 to 300 mm, and the difference in the extent to which the trunnion shaft and pipes expand when heated. To solve this problem, the inventor invented a structure in which a window is provided on the furnace side, i.e. the side that is attached to the furnace, of a trunnion ring so that the vertical pipe and manifold can be easily welded together therethrough (Japanese Patent Publication No. 72,113 of 1981). But this structure still involved the danger that the oxygen flowing from the horizontal pipe to the vertical pipe, whirls and is liable to cause combustion.
It is well-known that the refractory lining of the converter vessel wears out as the number of heats the vessel undergoes increases. Especially toward the end of a furnace operating program, the refractory lining becomes so thin that the steel shell temperature rises greatly. It can reach 700.degree. to 800.degree. C. where the lining wear is heavy. In extreme cases, the steel shell melts away which causes an outflow of molten steel. Especially, the lining on the inside of that portion of the steel shell to which the shaft of the trunnion ring is attached is in constant contact with slag (having a high brick-eroding power), irrespective of the angle through which the vessel is tilted. Located, in addition, where castable flame gunning is difficult to apply, this portion has a greater chance than elsewhere of causing a dangerous metal outflow.
In the conventional vessel having an oxygen passage running through its trunnion, the overheating or erosion of the steel shell on the inside thereof can exert a similar thermal or chemical effect on the trunnion, thereby giving rise to explosive oxygen-induced combustion.
With the conventional vessel, furthermore, the horizontal pipe extends from a rotary joint, and is supported midway by a flange fastened to the end surface of the trunnion ring shaft. When the furnace is in operation, the shaft becomes hot under the effect of the heat from the vessel, whereas the horizontal pipe remains not quite so hot, giving rise to a difference in the extent of thermal expansion. This expansion difference can cause a leakage from the pipe-end joint or a bend in the vertical pipe. The leakage and bend, in turn, bring the oxygen in contact with dust, rust or such combustible gases as LPG, resulting in the danger of explosion, either inside or outside the trunnion.